In recent years, the capacity of storage batteries has been greatly increased, and the utilization of storage batteries for the storage of power consumed in homes, stores, buildings and the like has been examined. In such storage batteries, power is previously stored, and thus the power can be discharged at any time (that is, the power can be supplied). Hence, for example, when system power (power supplied from an electric power company; the same is true in the following description) consumed in, for example, a home, a store or the like is instantaneously increased, the power is supplied by discharge of a storage battery, and can be utilized to reduce the instantaneous consumption of the system power. A storage battery can also be utilized as an emergency power supply source, for example, when the supply of the system power to a home, a store or the like is stopped due to a disaster or the like.
Incidentally, a storage battery cannot discharge power beyond the amount of power stored previously in the storage battery. Hence, when a user discharges a storage battery, it is possible that the storage battery cannot discharge power beyond the expected time.
Hence, for example, patent document 1 discloses a power supply system that predicts, based on a voltage value of a storage battery being discharged, a time in which the storage battery can discharge power, and that displays it. In particular, in this power supply system, based on a time required to reduce the voltage value only by a predetermined magnitude, a method of predicting the time in which the storage battery can discharge power is modified, and thus the time in which the storage battery can discharge power is accurately predicted.